Aqueous,alkaline,cyanide-free bath for the galvanic deposition of zinc and zinc alloy coatings

ABSTRACT

The invention relates to an aqueous, alkaline cyanide-free electrolyte bath for de-positing zinc and zinc alloy coatings on substrate surfaces comprising (a) a source for zinc ions and optionally a source for further metal ions, (b) hydroxide ions, (c) a polymer of general formula I which is soluble in the bath and (d) at least one pyridinium compound of general formula II or III. The electrolyte bath is suitable for the galvanic deposition of bright and even zinc and zinc alloy coatings.

FIELD OF THE INVENTION

The present invention relates to an aqueous, alkaline galvanic bathwithout addition of cyanide ions as complexing agents for the depositionof zinc and zinc alloy coatings, which bath contains as additivesbis-(N,N-diaminoalkyl)urea-α,ω-dihaloalkyl copolymers or oligomers and3-carbamoyl pyridinium compounds quaternized in the 1-position.Furthermore, the invention relates to a process for the deposition ofbright and even zinc and zinc alloy coatings in which the bath is used.

BACKGROUND OF THE INVENTION

The zinc deposition from cyanide-containing alkaline solution has had asignificant market share for many years. However, increasingly stringentstatutory requirements regarding the disposal of used zinc and zincalloy electrolyte baths and the consequent strict control regardingwaste water have resulted in increased interest in cyanide-free zinc andzinc alloy electrolytes.

Such metal coatings are used for improving corrosion properties and forachieving certain optical properties. Thus, the automotive industry hasused electroplated zinc for decades in order to provide highlycorrosion-resistant coatings at reasonable cost.

Cyanide-free zinc electrolytes and corresponding alloy baths can beclassified into two types of baths, namely weakly acidic zincelectrolytes (containing zinc chloride or zinc sulfate) and alkalinezinc electrolytes. Weakly acidic zinc baths result in the deposition ofa uniformly bright zinc layer. However, they have the disadvantage thattheir current efficiency is always 100% across a wide range of currentdensities. In the case of substrates having a simple shape, this may beadvantageous since the electric current is used only for the depositionof zinc. However, in the case of substrates having a complex geometry,this results in excessively thick zinc layers in areas of high currentdensity and to thin zinc layers in areas of low current density.

The ratio of the zinc layer thickness in the area of high currentdensity to the zinc layer thickness in the area of low current densityis referred to as layer thickness distribution and should ideally be 1(scattering coefficient). From a technical and functional point of view,the zinc layer on the substrate should have the same or approximatelythe same layer thickness across the entire substrate and should havehigh brightness.

A good layer thickness distribution may be achieved by lowering thecurrent efficiency in the area of high current density while the currentefficiency is maintained in the area of low current density. So far,this kind of equalizing the zinc layer thickness across a wide range ofcurrent densities has been achieved in the deposition of zinc fromalkaline, cyanide-free electrolytes.

Alkaline zinc electroplating baths are generally constituted on thebasis of an aqueous solution of zincate ions in the presence of alkalimetal hydroxides. DE 25 25 264 and U.S. Pat. No. 3,884,774 describe suchelectrolytes; however, the zinc layers obtained according to thesedocuments do not show a uniform layer thickness distribution.

The state of the art contains numerous suggestions for improving thelayer thickness distribution by addition of suitable additives.

Such additive systems are described in U.S. Pat. No. 5,405,523, U.S.Pat. No. 5,435,989, DE 19 50 9713 and U.S. Pat. No. 4,030,987.

EP 1 114 206 B1 describes a formulation consisting of quaternaryderivatives of pyridinium-3-carboxylic acid, copolymers consisting ofN,N-bis-[3-(dialkylamino)-alkyl]ureas with α,ω-dihaloalkanes and anaromatic aldehyde, which are characterized in that the formation ofbubbles frequently described in connection of the deposition of zinc canbe avoided. Further copolymers of the aforementioned type are describedin U.S. Pat. No. 5,405,523, U.S. Pat. No. 5,435,898 and WO 2004/044269A2. Apart from the aforementioned ingredients, WO 2004/044269 A2 usesreducing sugars in order to obtain bright depositions. A disadvantage ofthis method is the high concentration of reducing sugars which resultsin increased COD and TOC contents in the effluent water.

The copolymers described in EP 1 114 206 B1, U.S. Pat. No. 5,405,523 andU.S. Pat. No. 5,435,898 are used as brightening agents together with thecommercially readily available quaternized derivatives of nicotinicacid, in particular, N-benzyl-nicotinate.

The use of 1-benzyl-3-carbamoyl-pyridinium-chloride forcyanide-containing alkaline zinc electrolytes is described in “KinzokuHyomen Gijutsu” (1980), 31, p. 244-248.

U.S. Pat. No. 4,071,418 describes a bath formulation consisting of aquaternary pyridinium derivative and a cationic copolymer of a diaminewith 1,3-dihalopropane-2-ol.

Despite the aforementioned suggestions, the electroplating industrystill has, in view of increasingly stringent economic and ecologicalrequirements, a constant need for improved alkaline, cyanide-free zincand zinc alloy electrolytes which are characterized, on one hand, byreduced amounts of additives and improved layer thickness distributionas well as, on the other hand, increased current efficiency and goodbrightness. Apart from the aforementioned aspect of layer thicknessdistribution, in times of steadily increasing energy costs, currentefficiency plays an important role since it is inversely proportional toinvestment and operational costs.

DESCRIPTION OF THE INVENTION

It is the object of the invention to provide zinc and zinc alloyelectrolytes which result in zinc and zinc alloy layers having highbrightness and good or improved layer thickness distribution at highcurrent efficiency.

It has now been found that, by combination of the copolymers known fromEP 1 114 206 B1, U.S. Pat. No. 5,405,523 and U.S. Pat. No. 5,435,898with suitable brightening agents, it is possible to obtain electrolytesresulting in the deposition of zinc and zinc alloy layers withsurprisingly improved layer thickness distribution, improved brightnessand increased current efficiency. In particular, it has been found thatthe use of pyridine-3-carboxylic acid amides as brightening agentsresults in electrolyte compositions which are characterized by highbrightness, improved layer thickness distribution and increased currentefficiency.

Thus, the invention provides an aqueous, alkaline, cyanide-freeelectrolyte bath for the deposition of zinc and zinc alloy coatings onsubstrate surfaces, which bath comprises the following components:

a) a source of zinc ions and, optionally, a source of further metalions,b) hydroxide ions,c) a polymer which is soluble in the bath of the general formula I

wherein

-   -   m represents an integer of 1 to 5, preferably 2 to 5, or 1 to 4,        more preferably 2 to 3,    -   n represents an integer greater than 1, preferably greater than        2,    -   R1, R2, R3, R4 may be the same or different and each represents        a substituted or unsubstituted hydrocarbon residue having 1 to 6        carbon atoms, preferably methyl, ethyl, hydroxyethyl or        —CH₂CH₂(OCH₂CH₂)_(y)—OH, wherein y lies between 0 and 6,    -   R5 represents (CH₂)_(p), wherein p represents an integer of 2 to        12, preferably a methylene or propylene group or a        —(CH₂)₂—O—(CH₂)₂— or —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— group and    -   X⁻ represents a counter ion, preferably halide or pseudo-halide;        and        d) at least one pyridinium compound of general formula II or Ill

wherein

-   -   R₁ represents a substituted or unsubstituted, saturated or        unsaturated, aliphatic or araliphatic hydrocarbon residue having        1 to 12 carbon atoms,    -   R₁′ represents a divalent, substituted or unsubstituted,        saturated or unsaturated, aliphatic or araliphatic hydrocarbon        residue having 1 to 12 carbon atoms,    -   X₁ and X₂ represent NR_(x)R_(y), wherein R_(x) and R_(y) may be        the same or different and represent hydrogen or linear or        branched alkyl groups having 1 to 12 carbon atoms, and    -   Y⁻ is a counter ion.

In a preferred embodiment, R₁ in formula II represents substituted arylof the following formulae R1a to R1I:

wherein FG represents a residue selected from the group consisting ofcarboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy,hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl,3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen andhalogens, selected from fluorine, chlorine and bromine,and R₁′ in formula III represents but-2-enyl, but-2-ynyl or aryl of thefollowing formulae R1′a to R1′ r:

wherein FG represents a residue selected from the group consisting ofcarboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy,trifluoromethyl residues, hydrogen and halogens, selected from fluorine,chlorine and bromine, wherein all rings or individual fused rings may besubstituted.

Preferably, residues R₁ and R₁′ in formulae II and III are bonded to thepyridinium residue via a methylene group.

Preferred araliphatic hydrocarbon residues are, for example, benzyl(R1a) and naphthyl methyl (R1b).

In the context of the present invention, fluorides, chlorides andbromides may be used as halides. Furthermore, the bath according to theinvention may contain compounds, which are similar, with respect totheir physical and chemical properties, to the halides, i.e., so-calledpseudo-halides. Such pseudo-halides are known to the skilled person assuch and are described, for example, in Römpp-Lexikon, Chemie, 10^(th)edition, page 3609. In the context of the present invention,pseudohalides also comprise residues such as mesitylate and triflate.

The soluble polymers of general formula I contained in the bath may beobtained according to EP 1 114 206 B1 by reaction ofN,N-bis-[(dialkylamino)-alkyl]-ureas with α,ω-dihaloalkanes. Aparticularly preferred copolymer of this class is, apart from thecompounds described in EP 1 114 206 B1, Mirapol™ WT available fromRhodia or Lugalvan™ P available from BASF.

The polymer of formula I is contained in the bath according to theinvention preferably in an amount of 0.1 to 50 g/l, more preferably 0.25to 10 g/l. The bath may contain a combination of different solublepolymers of general formula I.

The electroplating baths according to the invention contain an inorganicalkaline component, preferably a hydroxide of an alkali metal and,particularly preferably, sodium hydroxide, potassium hydroxide and/orlithium hydroxide, in order to adjust the pH of the bath to at least 10and preferably to at least 11. To this end, amounts of 50 to about 250g/l, preferably 90 to 130 g/l of the alkaline component may be used.

The electroplating baths according to the invention generally containzinc ions at concentrations ranging from about 0.1 to about 100 g/l,concentrations of 4 to 30 g/l being preferred. The zinc ion may bepresent in the bath according to the invention in the form of a solublesalt, for example zinc oxide, zinc sulfate, zinc carbonate, zincacetate, zinc sulfamate, zinc hydroxide, zinc tartrate.

As alloying metal, the baths according to the invention contain about0.1 to 50 g/l of metal ions, suitable metal salts are hydroxides,sulfates, carbonates, ammonium sulfates, sulfamates, acetates, formatesand halides, preferably chloride and bromide. Suitable alloying metalsare preferably cobalt, nickel, manganese and/or iron. The concentrationof the alloying metal ions in the baths according to the invention maybe varied across a wide range and preferably is 0.01 to 100 g/l. Sincedifferent types of alloys require different contents of alloying metals,for example in order to improve protection against corrosion, thisconcentration varies from metal ion to metal ion.

Preferably, the baths according to the invention contain about 0.1 to 50g/l of nickel ions as alloying metal. Suitable nickel salts are nickelhydroxide, nickel sulfate, nickel carbonate, ammonium nickel sulfate,nickel sulfamate, nickel acetate, nickel formate and nickel halides.

In a preferred embodiment, the electrolyte bath contains zinc in anamount of 0.1 to 30 g/l and cobalt in an amount of 10 to 120 mg/l,nickel in an amount of 0.3 to 3 g/l, manganese in an amount of 10 to 100g/l and/or iron in an amount of 10 to 120 mg/l.

The electrolyte baths according to the invention contain theaforementioned aromatic heterocyclic nitrogen-containing compounds ofgeneral formulae II and III for substantial improvement of leveling andbrightness properties of the deposited layers across a wide range ofcurrent densities. Therefore, the compounds of formulae II and III arehereinafter referred to as brightening agent according to the invention.

Preferred compounds of formulae II and III are1-benzyl-3-carbamoyl-pyridinium-chloride,1-(2′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(2′-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(2′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(2′-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(2′-carbamoylbenzyl)-3-carbamoyl-pyridinium-chloride,1-(3′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(3′-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(3′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(3′-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(3′-carbamoyl-benzyl)-3-carbamoyl-pyridinium-chloride,1-(4′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(4′-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,1-(4′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(4′-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,1-(4′-carbamoylbenzyl)-3-carbamoyl-pyridinium-chloride, (1‘-methyl-naphthyl)-3-carbamoyl-pyridinium-chloride,1-(1′methyl-naphthyl)-3-carbamoyl-pyridinium-bromide,1-(1’-methyl-naphthyl)-3-carbamoyl-pyridinium-fluoride,1,1′-(but-2-enyl)-3,3′-biscarbamoyl-bispyridinium-dichloride,1,1′-(but-2-enyl)-3,3′-bis-carboxy-bispyridinium-dichloride,1-allyl-3-carbamoyl-pyridinium-chloride,1-allyl-3-carboxypyridinium-chloride,1-propargyl-3-carbamoyl-pyridinium-chloride,1,1′-(but-2-ynyl)-3,3′-bis-carbamoyl-bispyridinium-dichloride,1,1′-(but-2-ynyl)-3,3′-bis-carboxy-bis-pyridinium-dichloride,1,1′-(xylenyl)-3,3′-bis-carbamoyl-bis-pyridinium-dibromide,1-(3′-sulfopropyl)-3-carbamoyl-pyridinium-betaine as well as thecorresponding bromides, fluorides, iodides and pseudo-halides (forexample, triflates, tosylates) of the aforementioned compounds.

The brightening agents can be readily prepared by reacting thecorresponding nicotinic acid amide derivatives with the correspondingbenzyl halides in a suitable solvent, such as ethanol, propanol,iso-propanol, butanol, iso-butanol, methanol or their mixtures, DMF,DMAc; NMP, NEP, in substance or in an aqueous medium, while heatingunder normal or increased pressure. The reaction times required rangefrom 1 to 48 hours, depending on the starting material used. In thisconnection, apart from conventional sources of heat, a microwave ovenmay be used. The pyridinium compounds obtained can either be useddirectly as the aqueous or alcoholic reaction solution or they can beisolated after cooling by filtration or by removal of the correspondingsolvent. The compounds can be purified by recrystallization from asuitable solvent such as ethanol, precipitation or columnchromatography.

The bis-pyridinium compounds of general formula II can be preparedaccording to U.S. Pat. No. 6,652,728.

The compounds of formula II or Ill can be used alone or as a mixture ata concentration of 0.001 to 20 WI, preferably of 0.001 to 10 g/l. Thebath may contain a combination of pyridinium compounds of formulae IIand III.

The baths according to the invention may be prepared according toconventional methods, for example by adding the specific amounts of theaforementioned components to water. The amount of the basic component,such as sodium hydroxide, should be sufficient to achieve the desired pHof the bath of at least 10 and preferably above 11.

The baths according to the invention deposit a bright, even and ductilezinc or zinc alloy layer at any conventional temperature of about 15° C.to 50° C., preferably 20° C. to 30° C., more preferably about 25° C. Atthese temperatures, the baths according to the invention are stable andeffective over a wide range of current densities of 0.01 to 10 A/dm²,preferably 0.5 to 4 A/dm².

The baths according to the invention can be used in continuous orbatch-wise mode and the components will have to be replaced from time totime. The components of the bath can be added alone or in combination.Moreover, depending on the type and the properties of the zinc and thezinc alloy baths to which the substances are added, they may be variedacross a wide range.

Table 1 shows, according to a particularly preferred embodiment, theinfluence with respect to the layer thickness (and thus currentefficiency), brightness and layer thickness distribution in theelectrolytes according to the invention for deposition of a zinc layer(using 10⁴ mmol/l of pyridinium compound and a polymeric additiveaccording to Preparation Example 2.2 of EP 1 114 206 B1):

TABLE 1 Layer Layer thickness thickness Layer [μm] [μm] thickness Ex.Pyridinium compound Brightness j = 3.0 A/dm² j = 0.5 A/dm² coefficient 11-benzyl-3-carboxy- +++ 3.84 2.41 1.59 pyridinium-chloride* 21-benzyl-3-carbamoyl- +++ 4.74 3.76 1.26 pyridinium-chloride 31-(4′-methoxy-benzyl)-3- +++ 4.20 3.18 1.32 carbamoyl-pyridinium-chloride 4 1-(4′-trifluoromethyl-benzyl)- +++ 4.98 3.71 1.343-carbamoyl-pyridinium- chloride 5 1,1′-(xylenyl)-3,3′- ++ 4.80 3.181.51 biscarbamoyl-bispyridinium- chloride 6 1-(4′-chloro-benzyl)-3- +++4.20 3.15 1.33 carbamoyl-pyridinium- chloride 7 1-benzyl-3-N,N- +++ 4.152.99 1.39 dimethylcarbamoyl- pyridinium-chloride *Comparative Exampleaccording to Example 13 of EP 1 114 206 B1

As Table 1 clearly shows, the novel electrolytes according to theinvention show markedly better layer thickness distributions while thecurrent efficiency is increased at the same time. In the areas of bothhigh and low current density, there are achieved current efficiencieswhich are 10 to 30% (in the area of high current density) or 30 to 50%(in the area of low current density) higher compared to the classicpyridinium compound. Especially the much higher current efficiencies inthe area of low current density are very interesting in connection withapplications using drum electroplating methods.

The formulation according to the invention of the aforementionedpyridinium compounds (which are known from U.S. Pat. No. 4,071,418) withthe aforementioned copolymers of general formula I results in unexpectedadvantageous properties of the deposited layers. Table 2 shows thesesynergistic effects of the electrolyte compositions according to theinvention:

TABELLE 2 Layer Layer thickness thickness Layer [μm] [μm] thickness Ex.Formulation Brightness j = 3.0 A/dm² j = 0.5 A/dm² coefficient 8Formulation according to +++ 4.9 3.7 1.32 the invention with 100 mg/l of1-benzyl-3-carbamoyl- pyridinium-chloride 9 Formulation according to +5.4 2.3 2.35 Example 6 of U.S. Pat. No. 4,071,418 with 100 mg/l1-benzyl-3- carbamoyl-pyridinium- chloride instead of sodium nicotinate10 Formulation according to + 6.1 3.3 1.85 Example 6 of U.S. Pat. No.4,071,418

As Table 2 shows, the formulations according to U.S. Pat. No. 4,071,418do achieve high current efficiencies at high current density; however,both the brightness and the layer thickness distribution coefficientobtained with these electrolytes are significantly worse than with theformulations according to the invention. Actually, the pyridiniumcompounds of general formula II and III give worse results incombination with the cationic polymers described in U.S. Pat. No.4,071,418 than the classic, widely used benzyl nicotinate.

A further advantage of the electrolytes according to the invention,compared to the electrolyte of EP 1 114 206 B1 is the surprisingly lowerconsumption of the quaternized nicotinamide derivatives according to theinvention, compared to the N-benzyl-nicotinate. As Application Example12 shows, the consumption of pyridinium compounds acting as brighteningagent in the electrolytes according to the invention is significantlylower and thus more economical than the conventionally used pyridiniumderivatives based on nicotinic acid.

Apart from the additives mentioned above, the baths according to theinvention may contain known levelling agents such as3-mercapto-1,2,4-triazole and/or thiourea, thiourea frequently beingpreferred.

In principle, the electrolyte bath according to the invention maycontain additional brightening agents from the group of sulphurcompounds, aldehydes or bisulfite adducts thereof, ketons, amines,polyvinyl alcohol, polyvinyl pyrrolidone, proteins or reactions productsof halohydrines with aliphatic or aromatic amines, polyamines orheterocyclic nitrogen compounds and mixtures thereof. As additionalbrightening agents, there may be used, in particular, aromatic aldehydesfrom the group of 4-hydroxybenzaldehyde,4-hydroxy-3-methoxy-benzaldehyde, 3,4-dimethoxy-benzaldehyde,3,4-methylenedioxy-benzaldehyde, 2-hydroxy-benzaldehyde and mixtures aswell as bisulfite adducts thereof, in an amount of 0.001 to 1.0 g/l.

Surprisingly, it was found that, with the electrolytes according to theinvention, the conventional use of aromatic aldehydes or their bisulfiteadducts as additional brighteners, for example 4-hydroxybenzylaldehyde,4-hydroxy-3-methoxybenzaldehyde, 3,4-dimethoxybenzaldehyde,3,4-methylenedioxybenzaldehyde, 2-hydroxybenzaldehyde or mixturesthereof as well as bisulfite adducts thereof, is unnecessary.

In a preferred embodiment, the electrolyte bath according to theinvention thus contains no aromatic aldehydes or their bisulfite adductsas additional brighteners, in particular, it contains no4-hydroxybenzylaldehyde, 4-hydroxy-3-methoxybenzaldehyde,3,4-dimethoxybenzaldehyde, 3,4-methylenedioxybenzaldehyde or2-hydroxybenzaldehyde or bisulfite adduct thereof.

The electrolyte bath according to the invention may contain a complexingagent or a water softening agent. The complexing agent is preferably achelate forming agent, which is preferably present in an amount of 2 to200 g/l.

The electrolyte bath according to the invention can also contain, asleveling agent, a sulfur compound, for example,3-mercapto-1,2,4-triazole and/or thiourea, preferably in an amount of0.01 to 0.50 g/l.

The aqueous, alkaline baths according to the invention can generally beused for all types of substrates on which zinc and zinc alloys can bedeposited. Examples of suitable substrates are soft steel, spring steel,chromium steel, chromiummolybdenum steel, copper, copper/zinc alloys.

Therefore, the invention also provides a process for the galvanicdeposition of zinc and zinc alloy coatings on conventional substrates,wherein the electrolyte bath according to the invention is used. In theprocess according to the invention, the deposition of coatings ispreferably carried out at a current density of 0.01 A/dm² to 10 A/dm²and at a temperature in the range of 15 to 50° C., preferably 20 to 30°C., more preferably about 25° C.

The process according to the invention may be carried out, for example,as barrel electroplating process when applied to small pieces and as arack electroplating process when applied to larger pieces. The processinvolves the use of anodes, which may be soluble, for example, zincanodes, which may serve as zinc ion source at the same time so that thezinc deposited on the cathode is replaced by dissolution of zinc fromthe anode.

However, insoluble anodes (for example, platinized titanium mixed oxideanodes) may also be used, in which case the zinc ions and/or furthermetal ions removed from the electrolyte by deposition of the alloy haveto be added to the electrolyte in other ways, for example by using azinc dissolution container.

As generally possible in electroplating, the process according to theinvention, too, can be carried out with injection of air, with orwithout agitation of the substrate, which has no negative effects on thecoatings obtained. In order to avoid or reduce the oxidation ofadditives, the electrode regions may be separated or membrane anodes maybe used.

The current source may be a conventional rectifier or pulse rectifier.

EXAMPLES

The following examples illustrate the invention, but the invention isnot limited thereto.

Preparation Example 1 Synthesis of1-(4′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride

In a 100 ml round-bottom flask with reflux condenser, 60 ml of water,9.2 g of nicotinic acid amide (98%) (0.0738 mol), 11.68 g of4-methoxybenzylchloride (99%) (0.07378 mol) are heated under reflux for24 hours. After completion of the reaction, the water is removed invacuo and the residue is taken up in 200 ml of ethanol and heated underreflux for another hour. The reaction mixture is then cooled to 4° C.and the white solid obtained is removed by filtration and dried invacuo. This yielded 16.92 g of a white solid (82.26% of the theoreticalyield).

Preparation Example 2 Synthesis of1-(4′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride

In a 100 ml round-bottom flask with reflux condenser, 60 ml of ethanol,10 g of nicotinic acid amide (98%) (0.0802 mol), 13.05 g of4-chloro-benzylchloride (99%) (0.0802 mol) are heated under reflux for24 hours. After completion of the reaction, the solid residue is heatedin an ethanol/methanol mixture for another 15 minutes and then cooled to4° C. The solid obtained is removed by filtration and dried in vacuo.This yielded 18.82 g of a white solid (82.87% of the theoretical yield).

Preparation Example 3 Synthesis of1,1′-(xylenyl)-3,3′-bis-carbamoyl-bis-pyridinium-dichloride

In a 100 ml round-bottom flask with reflux condenser, 60 ml of ethanol,10 g of nicotinic acid amide (98%) (0.0802 mol), 7.16 g ofα,α′-dichloro-p-xylene (98%) (0.0401 mol) are heated under reflux for 24hours. After completion of the reaction, the solid residue is heated in200 ml of an ethanol/methanol mixture for another 15 minutes and thencooled to 4° C. The resulting solid is removed by filtration and driedin vacuo. This yielded 12.29 g of a white solid (73.13% of thetheoretical yield).

Preparation Example 4 Synthesis of1-(4′-trifluoromethyl-benzyl)-3-carbamoyl-pyridinium-chloride

In a 100 ml round-bottom flask with reflux condenser, 80 ml of water,3.11 g of nicotinic acid amide (98%) (24.93 mmol), 4.95 g ofα-chloro-α,α,α-trifluoro-paraxylene (98%) (24.93 mmol) are heated underreflux for 24 hours. After completion of the reaction, the reactionmixture is concentrated in vacuo and the resulting solid is dried invacuo. This yielded 5.99 g of a white solid (75.82% of the theoreticalyield).

Preparation Example 5 Synthesis ofbenzyl-3-carbamoyl-pyridinium-chloride

In a 100 ml round-bottom flask with reflux condenser, 60 ml of ethanol,10 g of nicotinic acid amide (98%) (0.0802 mol), 10.252 g of benzylchloride (99%) (0.0802 mol) are heated under reflux for 24 hours. Aftercompletion of the reaction, the reaction mixture is cooled to 4° C. andthe resulting solid is removed by filtration and re-crystallized from 1liter of ethanol. This yielded 19.00 g of a white solid (95.33% of thetheoretical yield).

Preparation Example 6 Synthesis of1-benzyl-3-N,N-dimethylcarbamoyl-pyridinium-chloride

Into a 50 ml round bottom flask with reflux condenser are charged 1 g ofpyridine-3-N,N-dimethyl-carboxylic acid amide (6.658 mmol), 0.841 g ofbenzylchloride (99%) (6.658 mmol) in 10 ml of DMF and heated for 12hours at 120° C. After completion of the reaction, the excess solvent isremoved in vacuo and the crude product is extracted for a prolonged timewith water/ethyl acetate. The resulting ethyl acetate phase is discardedand the aqueous phase is concentrated in vacuo. The resulting solid isdried in oil pump vacuum. This yielded 1.8 g of a caramel color product(97.7% of the theoretical yield).

Application Example 1 Comparative Example according to EP 1 114 206 B1

An electrolyte having the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH   25 mg/l1-benzyl-3-carboxy-pyridinium-chloride   1 g/l a polymeric additiveaccording to Preparation Example 2.2 of EP 1 114 206 B1 (amount statedis relative to solid content)

250 ml of the electrolyte are filled into a Hull cell. A steel anode isused. The cathode sheet is coated for 15 minutes at 1 A. Aftercompletion of the reaction, the sheet is rinsed and dried withcompressed air. The measurement of layer thickness is carried out at twopoints (3 cm from the bottom edge and 2.5 cm from the right- andleft-hand edge) at high (3 A/dm²) and low current density (0.5 A/dm²).

The thickness layer coefficient is the ratio of the layer thickness athigh current density and the layer thickness at low current density.

A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 3.84 2.41 1.59

Application Example 2

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH   25 mg/l1-benzyl-3-carbamoyl-pyridinium-chloride   1 g/l a polymeric additiveaccording to Preparation Example 2.2 of EP 1 114 206 B1 (amount statedis relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.74 3.76 1.26

Application Example 3

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH 27.8 mg/l1-(4′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride   1 g/l apolymeric additive according to Preparation Example 2.2 of EP 1 114 206B1 (amount stated is relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.20 3.18 1.32

Application Example 4

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH 31.7 mg/l1-(4′-trifluoromethyl-benzyl)-3-carbamoyl-pyridinium-chloride   1 g/l apolymeric additive according to Preparation Example 2.2 of EP 1 114 206B1 (amount stated is relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.98 3.71 1.34

Application Example 5

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH 41.9 mg/l1,1′-(xylenyl)-3,3′-biscarbamoyl-bispyridinium-dichloride   1 g/l apolymeric additive according to Preparation Example 2.2 of EP 1 114 206B1 (amount stated is relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient ++ 4.80 3.18 1.51

Application Example 6

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂  120 g/l NaOH 28.3 mg/l1-(4′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride   1 g/l a polymericadditive according to Preparation Example 2.2 of EP 1 114 206 B1 (amountstated is relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] Layer thickness [μm] thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.20 3.15 1.33

Application Example 7

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂ 120 g/l NaOH 27. mg/l1-benzyl-3-N,N-dimethylcarbamoyl-pyridinium-chloride 1 g/l a polymericadditive according to Preparation Example 2.2 of EP 1 114 206 B1 (amountstated is relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] thickness [μm] Layer thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.15 2.99 1.39

Application Example 8

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂ 120 g/l NaOH 100 mg/l1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l a polymeric additiveaccording to Preparation Example 2.2 of EP 1 114 206 B1 (amount statedis relative to solid content)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] thickness [μm] Layer thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.90 3.70 1.32

Application Example 9 Comparative Example according to U.S. Pat. No.4,071,418 with 1-benzyl-3-carbamoyl-pyridinium-chloride

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂ 120 g/l NaOH 100 mg/l1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l a polymeric additiveaccording to Preparation Example 1 of U.S. Pat. No. 4,071,418 (amountstated is relative to solid content)A bright deposition with the following layer thicknesses was obtained:

Layer Layer thickness [μm] thickness [μm] Layer thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient + 5.40 2.30 2.35

Application Example 10 Comparative Example according to U.S. Pat. No.4,071,418

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂ 120 g/l NaOH 200 mg/l1-benzyl-3-carboxy-pyridinium-chloride (N-benzyl nicotinate) 1 g/l apolymeric additive according to Preparation Example 1 of U.S. Pat. No.4,071,418 (amount stated is relative to solid content)A bright deposition with the following layer thicknesses was obtained:

Layer Layer thickness [μm] thickness [μm] Layer thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient + 6.10 3.30 1.85

Application Example 11

Application Example 1 is repeated with the exception that an electrolytehaving the following composition is used:

12.5 g/l Zn(OH)₂ 120 g/l NaOH 25 mg/l1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l Mirapol ™ WT (rel. 100%)A very bright deposition with the following layer thicknesses wasobtained:

Layer Layer thickness [μm] thickness [μm] Layer thickness Brightness j =3 A/dm² j = 0.5 A/dm² coefficient +++ 4.70 3.60 1.305

Application Example 12 Long-Term Experiment with a 5 Liter Bath forDetermining the Additive Consumption

In a comparative experiment, electrolytes having the followingcomposition are used:

12.5 g/l zinc oxide 130 g/l NaOH 20 g/l sodium carbonate 1 g/l 1 g/l ofa polymeric additive according to Preparation Example 2.2 of EP 1 114206 B1 (amount stated is relative to solid content) 25 mg/l a pyridiniumcompound (N-benzyl nicotinate or 1-benzyl-3-carbamoyl-pyridinium-chloride) 100 mg/l 3-mercaptotriazol 50 mg/lp-hydroxybenzaldehyde (active substance as bisulfite adduct)

The use of N-benzylnicotinate corresponds to the teaching of the priorart (Example 14 of EP 1 114 206 B1).

In order to compare the consumption of additives of the electrolyteaccording to the invention and the electrolyte according to the priorart, both electrolytes are used in a 5 liter bath as in the ApplicationExamples described above in order to electroplate Norton sheets. In thisexperiment, a Norton sheet is electroplated at 6 A for 30 minutes,whereafter the layer thickness and the visual appearance are evaluated.When the zinc and nickel contents which could be determined by titrationwith EDTA solution, were sufficient and the visual appearance of theNorton sheets was good and bright, the electroplating is continued. Atintervals of 50 Ah (10 Ah/l), a complete bath test is carried out,consisting of the Hull cell test (as described above) and thedetermination of the zinc and NaOH concentration. If too little zinc(target value: 10 g/l zinc oxide) or NaOH is present, the missing amountis added. After the brightness has decreased, the correspondingpyridinium compound is replenished.

Relative to 10,000 Ah, the following additive consumption of pyridiniumcompounds used as brightening agents was determined:

Consumption/ Entry Pyridinium compound 10 kAh Percent consumption 1N-benzyl nicotinate  20 g  100% (reference) (comparison) 21-benzyl-3-carbamoyl- 3.5 g 17.5% pyridinium-chloride

Application Example 13

An electrolyte having the following composition is used:

12 g/l ZnO 9.5 g/l nickel sulphate hexahydrate 120 g/l NaOH 30 g/ltetraethylenepentamine 0.1 g/l a polymeric additive according toPreparation Example 2.2 of EP 1 114 206 B1 (amount stated is relative tosolid content) 50 mg/l 1-benzyl-3-carbamoyl-pyridinium-chloride

250 ml of the electrolyte are filled into a Hull cell. A nickel anode isused. The cathode is electroplated at 1A for 15 minutes. Aftercompletion of the electroplating, the metal sheet is rinsed and driedwith compressed air. The layer thickness is measured at two points (3 cmfrom the bottom edge and 2.5 cm from the right- and left-hand edge) athigh (3 A/dm²) and low current density (0.5 A/dm²). The measurement ofthe nickel content is carried out at the same places. The measurement isdone by XRF and four points in each position so as to minimizemeasurement errors. The coating obtained was highly bright.

The following layer thicknesses and nickel contents were obtained:

Current density [A/dm²] Layer thickness [μm] Ni conc. [%] 3.0 6.7 15.10.5 2.6 13.1

Application Example 14

An electrolyte suitable for deposition of a zinc iron layer wasprepared. The electrolyte had the following composition:

12.5 g/l ZnO 120 g/l NaOH 50 mg/l iron (in the form of FeSO₄•7 H₂O) 25g/l sodium gluconate 1 g/l a polymeric additive according to PreparationExample 2.2 of U.S. Pat. No. 6,652,728 (rel. 100%) 100 mg/l1-benzyl-3-carbamoyl-pyridinium-chloride

A Hull cell sheet was coated for 10 minutes at 1 ampere. A very brightdeposition is obtained. The Hull cell sheet was rinsed and chromated ina commercially available black chromation for zinc iron layers (Tridur™black liquid ZnFe, Atotech). The chromated sheet showed good blackcoloration.

1. Aqueous, alkaline, cyanide-free electrolyte bath for the depositionof zinc and zinc alloy coatings on substrate surfaces, which bathcomprises the following components: a) a source of zinc ions and,optionally, a source of further metal ions, b) hydroxide ions, c) apolymer which is soluble in the bath of the general formula I

wherein m represents an integer of 1 to 5, n represents an integergreater than 1, R1, R2, R3, R4 may be the same or different and eachrepresents a substituted or unsubstituted hydrocarbon residue having 1to 6 carbon atoms or —CH₂CH₂(OCH₂CH₂)_(y)—OH, wherein y lies between 0and 6, R5 represents (CH₂)_(p), wherein p represents an integer of 2 to12 or a —(CH₂)₂—O—(CH₂)₂— or —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— group and X⁻represents a counter ion, and d) at least one pyridinium compound ofgeneral formula II or III

wherein R₁ represents a substituted or unsubstituted, saturated orunsaturated, aliphatic or araliphatic hydrocarbon residue having 1 to 12carbon atoms, R₁′ represents a divalent, substituted or unsubstituted,saturated or unsaturated, aliphatic or araliphatic hydrocarbon residuehaving 1 to 12 carbon atoms, X₁ and X₂ represent NR_(x)R_(y), whereinR_(x) and R_(y) may be the same or different and represent hydrogen orlinear or branched alkyl groups having 1 to 12 carbon atoms, and Y⁻ is acounter ion.
 2. Electrolyte bath according to claim 1, wherein R₁ informula II represents a substituted aryl residue of the followingformulae R1a to R1I:

wherein FG represents a residue selected from the group consisting ofcarboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy,hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl,3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen andhalogens, selected from fluorine, chlorine and bromine wherein all ringsor individual fused rings may be substituted.
 3. Electrolyte bathaccording to claim 1, wherein R₁′ in formula III represents but-2-enyl,but-2-ynyl or an aryl residue of the following formulae R₁′ a to R₁′r:

wherein FG represents a residue selected from the group consisting ofcarboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy,trifluoromethyl residues, hydrogen and halogens, selected from fluorine,chlorine and bromine, wherein all rings or individual fused rings may besubstituted.
 4. Electrolyte bath according to claim 1, wherein R₁ inFormula II and/or R₁′ in Formula III is/are bound to the pyridiniumresidue via a methylene group.
 5. Electrolyte bath according to claim 1,wherein Y⁻ in Formula II or III is a halide or pseudo-halide. 6.Electrolyte bath according to claim 1, wherein the polymer of generalformula I which is soluble in the bath is present in an amount of 0.1 to50 g/l.
 7. Electrolyte bath according to claim 6, wherein the polymer ofgeneral formula I which is soluble in the bath is present in an amountof 0.25 to 10 g/l.
 8. Electrolyte bath according to claim 1, wherein theat least one pyridinium compound of formula II or III is present in anamount of 0.001 to 20 g/l.
 9. Electrolyte bath according to claim 8,wherein the at least one pyridinium compound of formula II or III ispresent in an amount of 0.001 to 10 g/l.
 10. Electrolyte bath accordingto claim 1, containing a combination of pyridinium compounds of formulaeII and III.
 11. Electrolyte bath according to claim 1, containing acombination of different soluble polymers of general formula I. 12.Electrolyte bath according to claim 1, wherein the source of zinc ionsis zinc oxide or zinc hydroxide.
 13. Electrolyte bath according to claim1, wherein the concentration of zinc ions is from 0.1 to 100 g/l. 14.Electrolyte bath according to claim 13, wherein the concentration ofzinc ions is from 0.1 to 30 g/l.
 15. Electrolyte bath according to claim1, wherein the further metal ions are cobalt, nickel, manganese and/oriron ions.
 16. Electrolyte bath according to claim 15, wherein the zincis present in an amount of 0.1 to 30 g/l and the cobalt is present in anamount of 10 to 120 mg/l, the nickel is present in an amount of 0.3 to 3g/l, the manganese is present in an amount of 10 to 100 g/l and/or theiron is present in an amount of 10 to 120 mg/l.
 17. Electrolyte bathaccording to claim 1, containing alkali metal hydroxide as base. 18.Electrolyte bath according to claim 17, wherein the alkali metalhydroxide is lithium hydroxide, sodium hydroxide and/or potassiumhydroxide and is present in an amount of 50 to 250 g/l.
 19. Electrolytebath according to claim 1, wherein the pH of the bath is at least 10.20. Electrolyte bath according to claim 1, wherein the bath does notcontain additional brightening agents.
 21. Electrolyte bath according toclaim 1, containing a complexing agent or a water-softening agent. 22.Electrolyte bath according to claim 21, wherein the complexing agent isa chelate-forming agent.
 23. Electrolyte bath according to claim 21,wherein the complexing agent is present in an amount of 2 to 200 g/l.24. Electrolyte bath according to claim 1, wherein the bath contains asulfur compound as leveling agent.
 25. Electrolyte bath according toclaim 24, wherein the leveling agent contains 3-mercapto-1,2,4-triazoleand/or thiourea.
 26. Electrolyte bath according to claim 24, wherein thesulfur compound is present in an amount of 0.01 to 0.50 g/l.
 27. Processfor the galvanic deposition of bright and even zinc and zinc alloycoatings, comprising the step of immersing the substrate to be coatedinto a bath according to claim
 1. 28. Process according to claim 27,wherein the bath is operated at a current density of 0.01 to 10 A/dm².29. Process according to claim 27, wherein the bath is operated at atemperature of 15 to 50° C.
 30. Process according to claim 29, whereinthe bath is operated at a temperature of 25 to 35° C.
 31. Processaccording to claim 27, wherein the coatings are deposited on aconductive substrate by using a drum electroplating process.
 32. Processaccording to claim 27, wherein the coatings are deposited on aconductive substrate by using a rack electroplating process.
 33. Processaccording to claim 27, wherein a zinc coating is deposited on thesubstrate.
 34. Process according to claim 27, wherein a zinc alloycoating is deposited on the substrate.
 35. Process according to claim34, wherein a coating of a zinc alloy with one or more metals from thegroup consisting of cobalt, nickel, manganese and/or iron is depositedon the substrate.